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Biology 1b ­ Evolution
and Environment…read more

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Adapt and Survive
Desert animals have a large surface area compared to volume to reduce
water loss. They are efficient with water with little sweating and small
amounts of very concentrated urine. They are good in hot sandy
conditions too with their feet and sandy colour.
Arctic animals have a small surface area compared to volume to reduce
heat loss. They are well insulated with layers of blubber and thick fur and
are good in snowy conditions with big feet to spread out weight and
Plants living in the desert minimise water loss by having spines, having a
small surface area and storing water in the stem. They also maximise
water absorption by having long roots underground or having a large
surface area.
Some plants and animals are adapted to deter predators by armour like a
tortoises hard shell or thorns and sharp spines on plants. Other produce
poison ­ like bees and poison ivy. Others have warning colours like wasps
with their yellow and black stripes.…read more

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Populations and Competition
The size of any population depends on three main factors:
competition, disease and predation.
Competition ­ organisms compete with other species for the same
resources. Plants compete for light, water and nutrients. Animals
compete for territory, food, water and mates.
Disease ­ Infectious diseases kill off many members of a population,
but organisms that are fit and healthy will most likely survive.
Predation ­ If an organism gets eaten its population will decrease,
like humans eating too many cod.
Competition for the same resources means that a habitat can only
support a certain number of organisms. This determines the size of
the population. If there aren't many resources an organism will
need lots of space, but if there are loads of resources they only need
a smaller space.…read more

Slide 4

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Variation in Plants and Animals
Organisms from the same species will look slightly different e.g. hair
colour. These are called variations and there are two types of
variation: genetic variation and environmental variation.
An organisms characteristics are determined by the genes inherited.
Combining genes from two parents causes genetic variation. Eye
colour, blood group and inherited disorders (e.g. haemophilia or
cystic fibrosis) are only determined by genes.
Environmental variation covers a wide range of differences like
losing toes or getting a suntan or having yellow leaves.
Most characteristics e.g. Weight, height, skin colour, condition of
teeth, academic and athletic prowess are determined by a mixture
of genetic and environmental factors. For example, the maximum
height that an animal/plant may grow is determined by its genes,
but whether it grows tall depends on its environment (e.g. how
much food it gets).…read more

Slide 5

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Genes, Chromosomes and DNA
The nucleus contains your genetic information.
The human cell nucleus contains 23 pairs of chromosomes.
Chromosomes carry genes. Different genes control the
development of different characteristics.
A gene - a short length of the chromosome which is quite a
long length of DNA.
The DNA is coiled up to form the arms of the chromosome.…read more

Slide 6

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An ordinary cell can make a new cell by dividing in two. The new cell has
exactly the same genetic information ­ this is known as asexual
reproduction where there is only one parent so they are clones. The
chromosome splits down the middle to form two identical sets of `half-
chromosomes'. A membrane forms around them and the DNA replicates
itself to produce complete sets of chromosomes.
The gametes from the mother and the father become a fertilised egg and
this is why the offspring inherits features from both parents because the
gametes carry half the of the chromosomes each. This is why sexual
reproduction produces more variation than asexual reproduction.…read more

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